This invention relates to a filter media for apparatus for commercial or industrial use in removing particulate matter, such as dust, from a stream of gas, such as air, by cartridge filtration.
In dust filtering apparatus, a baghouse is used which, in the prior art, usually houses an array of cylindrical filter bags suspended from a tube sheet. However, in some prior art installations, an array of filter cartridges, instead of filter bags, have been used.
A dust filter bag is a tubular bag of cylindrical cross section, usually made of fabric which permits passage of air therethrough into the interior of the bag but obstructs passage of dust therethrough. The dust collects on the outer surface of the fabric and from time to time is removed, as by a blast of reverse air.
A filter cartridge, as distinguished from a filter bag, includes an inner perforated tubular sleeve or tube, usually of metal, which is surrounded by an annular filter media, usually of paper, for example, resin impregnated paper. In the prior art, the paper filter media has been pleated for the purpose of increasing the total surface area of the media and to permit the cartridge to be of shorter length than would otherwise be required.
The filter bags or filter cartridges, as the case may be, are suspended in a baghouse which is divided into two sections, a lower dust-laden air chamber, and an upper clean-air chamber. The two chambers are separated by a tube sheet having rows of spaced holes, each of which is in registry with one of the filter bags or filter cartridges. The dust-laden air is blown or drawn upwardly and passes through the wall of the filter bag or cartridge into the interior thereof. The dust does not pass through and collects on the outer surface of the fabric of the filter bag or on the outer surface of the pleated paper media of the cartridge. The dust-free air continues on, upwardly through the open mouths of the bags or cartridges through the holes in the tube sheet and into the upper or clean-air chamber.
Over a period of time, the collection of dust on the outer surface of the bag or cartridge, unless removed, would impede, and eventually prevent, flow of air through the wall and into the interior of the filter bag or cartridge.
The prior art has provided methods for removing the accumulation of dust from the outer wall. Pressurized air is blown in a reverse direction through the bag or cartridge. This is done by injecting a blast of air under pressure into the mouth of the bag to cause it to flow downwardly and outwardly through the fabric or paper wall, thereby to dislodge the dust accumulated on the outer surface of the wall and cause it to fall into a receptacle at the bottom of the lower chamber of the baghouse. A venturi is used to amplify the reverse air.
The prior art has also provided a pneumatic pulse jet system which provides continuous automatic cleaning of the baghouse but cleans only one row of bags or cartridge at a time. Using a timed cycle, a burst of compressed air is directed down through the venturi at the top of each bag in a single row. This induces clean air into the bag setting up a pneumatic shock wave inside. The air flow upwardly through the bag is momentarily stopped and the bag is flexed outwardly, causing accumulated dust particles to drop off into the collector hopper. Since only one row of bags is subjected to the blast of compressed air at a time, there is no interruption of air flow upwardly through the other filter bags or cartridges. This system provides a smooth operating dust control or material handling system.
Prior art filter cartridge systems have been capable of filtering relatively small concentrations of dust or fumes from slow moving air stream, but have not been capable of filtering large concentrations of dust from fast moving air streams. The reason for the inability of the prior art filter cartridge system to handle fast moving air streams carrying large concentrations of dust is the fact that the prior art system has used large diameter cartridge elements having a large number of deep closely-spaced pleats forming a large number of small-angled dust-collecting pockets. The dust becomes so lodged in the deep small-angle pockets that it cannot be effectively removed by the reverse jet air blast. This reduces the effective area of the filter media and has forced the prior art cartridges to have large areas of filter media for each cartridge element. Such large filter elements, when laden with dust become heavy and filter element replacement is made more difficult.
The efficiency and effectiveness of the filter cartridge can be increased by using a cartridge of relatively small diameter with filter media having a relatively small number of pleats of relatively short length, but substantially wider dust angles.
An important advantage of the small-diameter filter cartridge is that it may be installed in existing baghouses to replace the closely spaced filter bags now contained in such baghouses. As described previously herein, a typical filter bag has a diameter of about six inches. In contrast thereto, many prior art filter cartridge have an outside diameter of the order of twelve inches and thus cannot be used to replace filter bags in existing baghouses. Such baghouses may have as many as 500 filter bags in closely spaced rows and, it is an important practical advantage to be able to replace each small-diameter filter bag with a filter cartridge without having to replace the tube sheet.
The present application describes and claims mechanical attachment structure adapted for installing the small-diameter filter cartridge in baghouses, including existing baghouses in which the filter elements are closely spaced filter bags.
As used in the claims, the term "small-diameter filter cartridge" means a filter cartridge having a diameter of the order of six inches.